Basic achievements of soical development lie in the child's attainment of the interactive skills which enable him to become a progressively more adept partner in generating the patterns of interaction characteristic of human social encounters. This proposal is guided by a model of infant social development that stresses the continual interplay between the infant's experiences in social interaction and his attainment of interactive skills. The primary aims of the research are: (1) to describe the patterns of interaction infants generate with others, (2) to discover the interactive skills of the infant that contribute to such patterns, and (3) to understand how each skill originates in development and how each functions to mold still further development. The initial arena for discovering interactive skills (Study 1) lies in the attempts of 24 pairs of peers, either 18- or 24 months of age, to generate social interaction; whatever interaction peers manage must be attributed to the skills of children of their age. Observers record predefined behaviors that, when combined with videotaped records, provide a sequential listing of each child's behavior along a common time line and allow analyses of temporal correspondences in the two children's behavior. Study 2, a longitudinal inquiry, traces the developmental course of the interactive skills discovered in Study 1; the sequence in which the skills emerge and the social contexts in which they emerge are assessed. Forty infants are observed at 15, 18, 21, 24, and 30 months of age interacting with their mother, an unfamiliar woman, and a peer. Study 3 contrasts the interactive experiences and the skills achieved by 24-month olds who have grown up with or without an older sibling.